April 24 (Reuters) - An avian-borne virus outbreak on a California quail farm has fueled fears that the disease known as bird flu could spread, prompting investigators to continue their probe and five key export markets to bar imports of poultry from the state.

A state diagnostic laboratory confirmed on April 18 that a quail flock in Stanislaus County, California, tested positive for low-pathogenic avian influenza virus. It was later confirmed by a federal laboratory.

The virus, which commonly occurs in wild birds, is not considered a human health concern.

Yet news of the virus - particularly in a state that is home to two leading container ports heavily used for agricultural exports - has some of the world’s largest U.S. poultry consumers scrambling to protect themselves.

On Thursday, Hong Kong’s Centre for Food Safety announced a ban on the import of all poultry and poultry produced from Stanislaus County. Taiwan, too, has blocked chicken imports from California, while Japan has banned poultry slaughtered and eggs laid in California on or after March 24, according to U.S. Department of Agriculture data. Cuba has restricted imports of frozen or fresh poultry raised or processed in Stanislaus County on or after April 19.

And Russia’s state veterinary and phytosanitary service (VPSS) has banned poultry imports from California for 90 days due to the appearance of the bird flu, VPSS spokesman Alexei Alekseenko told Reuters on Wednesday.

The U.S. exported $5.53 billion worth of poultry meat and products in 2013, up from $5.46 billion in 2012, according to the U.S. Department of Agriculture.

Veterinarians and investigators from USDA and the California Department of Food and Agriculture are working together “to humanely euthanize birds,” CDFA spokesman Steve Lyle said. Together, he said, the agencies “are continuing to investigate this outbreak.”

SPORADIC CASES

Other cases of low-pathogenic avian influenza virus have been sporadically identified in the United States in recent years, according to USDA officials, including two instances in commercial meat turkey flocks in 2011 in Missouri and Minnesota.

The farm with the current outbreak, located near San Francisco, was quarantined after the H5 virus strain was detected, the World Organization for Animal Health (OIE) reported on its website. The farm, which has not been identified by name, had about 95,000 Japanese quail and some 21,000 Peking ducks, the OIE said.

The outbreak so far has affected two poultry buildings, with a layer house holding about 56,000 adult quail and a brooder house with about 39,000 quail.

AVOIDING CALIFORNIA

The export bans, even if temporary, are expected to have little impact on California’s chicken and poultry industry, which predominantly raises meat for the domestic market, industry analysts said.

But the news has caused logistical problems for some poultry producers outside of the Golden State which typically ship containers of frozen or chilled poultry meat or eggs through the ports of Oakland or Long Beach.

A Tyson Foods spokesman said in an email on Thursday it does not have any poultry plants in California, so none of its operations have been affected by the virus outbreak. But the company has adjusted its shipping to start using west coast ports outside of California, in order to maintain poultry deliveries to its export customers, said company spokesman Gary Mickelson.

Toby Moore, spokesman for the Poultry & Egg Export Council, said other poultry producers are also re-routing their cargo to ports in other states to avoid California altogether.

“Exporters are concerned,” Moore said. “Any transit restrictions means you have to make changes and start to work around your normal practices.” (Additional reporting by Eric M. Johnson in Seattle and Polina Devitt in Moscow; Editing by Richard Chang)